Download Peristalsis - Animal Nutrition

Lesson 2
How does food
move down
the oesophagus?
Journey of Food
Peristalsis
The muscles in the wall of the canal cause
rhythmic, wave-like contractions called
Peristalsis. This process can be visualized as
a squeezing action, forcing the food along.
Oesophagus
 Food moves on to
the stomach by
peristalsis.
Any Digestion?
 No digestion
Motility in the oesophagus
 The canal has layers of muscles in its walls:

Circular muscles

Longitudinal muscles
Peristalsis
circular
muscle contracts, the
longitudinal muscle
relaxes causing the gut
wall to constrict thus
 When the
squeezing and pushing the
food forward.
longitudinal
muscle contracts, the
circular muscle
relaxes and the gut
dilates becoming wider for
 When the
food to enter.
Circular muscles above the bolus contracts
Circular muscles below the bolus relaxes
http://www.westga.edu/~lkral/peristalsis/index.html
Digestion in the stomach
Overview
Role of Digestion
Large Intestine & Others
Mouth & Oesophagus
Gall Bladder &Pancreas
Stomach
Small Intestine
The last lesson
 The physical and chemical digestion in the
mouth
 The structure of oesphagus and stomach
 The process of peristalsis
How does the giraffe drink?
Giraffe
 Tallest animals in the world
 Range from 3m -5m tall
 Drinking – Going against gravity?
Your ideas?
Eat and drink in space?
 No gravity
 Eating and drinking –
possible in the
absence of gravity?
 If yes, Why?
 If no, Why?
An astronaut eating a
piece of Cornflake in
space.
Recall….
A closer look
Ss
Today’s lesson
The chemical digestive process in the stomach
Overview
Role of Digestion
Large Intestine & Others
Mouth & Oesophagus
Gall Bladder &Pancreas
Stomach
Small Intestine
Digestion in the stomach
 The stomach is a
muscular bag which
contracts and relaxes to
mix the food.
 In here:

Digestion
 Of only
PROTEINS
Peristalsis revisited
 How does peristalsis play a role in
the stomach?
 Continual contractions & relaxations
of stomach wall muscles result in a
churning action
 Physical digestion
 Breaks up food particles 
↑ SA / V of ingested food
 Mixes food well with gastric juice
for efficient enzymatic action
Picture from: http://wwwartsci.clarion.edu/biology/bbarnes/digestivesystem/stomach/stomach_peristalsis.gif
Stomach
 Main function:
store
food  turn it into liquid
(chyme)  release it
in small quantities at a
time to the rest of the
gut
 Stores food temporarily
for 3 to 4 hours.
 Contains
gastric glands: secrete gastric juice
that mixes with food to form chyme
 Gastric juice:

water + enzymes + hydrochloric acid

pH around 2.0
Function of Hydrochloric acid in the
stomach
Functions
Actions
Digestion
Activates the enzymes pepsin
Anti-bacterial
Kills harmful bacteria ingested with
food
Neutralisation
Neutralizes the alkaline saliva from
the mouth (i.e. stops the action of
salivary amylase)
Optimal pH
Lowers pH to pH 2 at which the
gastric enzymes work best
Conversion of inactive form of
enzymes to active form
 Both enzymes are secreted are produced as
inactive form – pepsinogen & prorennin
Hydrochloric acid
Pepsinogen
Pepsin
Hydrochloric acid
Prorennin
Rennin
Why must both enzymes be secreted in the
inactive form?
Enzymes (Proteases) in the stomach
Enzymes
Enzymatic actions
Substrate
Rennin
Pepsin
(Active)
Soluble milk
protein
(caseinogen)
Protein
Product
Insoluble
protein (casein)
Polypeptide
What we have learnt
Oesophagus
is a
Narrow, muscular tube
with
2 layers of muscles
outer
inner
Longitudinal
Circular
which are
Antagonistic
producing
Rhythmic, wave-like contractions
known as
Peristalsis
responsible for
Downward movement of food
into
Stomach
What we have learnt
Stomach
is a
Distensible, muscular bag
with
which produces
Gastric glands
Churning action
which secrete
resulting in
Gastric juice
Physical digestion
containing
HCl
activates
Enzymes
stops
Amylase action
kills
Bacteria
breaking food into
Smaller pieces
responsible for
Chemical digestion
such as
creates
Acidic medium
for effective
action by
Pepsin
digests
Proteins
into
Polypeptides
Rennin
Small intestines
converts
Caseinogen
into
Pyloric sphincter
into
Casein
making up part of
which passes through
Chyme